<!DOCTYPE html>
<html>
	<head>
		<title>函数参数</title>
		<meta charset="utf-8" />
	</head>
	<body>
		<script type="text/javascript">
			function sum(x,y){
				return x + y;
			}
			
			document.write(sum(2) + "<br/>");
			document.write(sum(2,5) + "<br/>");
			document.write(sum(2,5,9) + "<br/>");
		</script>
	</body>
</html>
